C++ Classes & Member Functions: inline, static, const, Nested Classes, Constant Data, Slides of Computer Science

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Classes

Member Qualifiers

Member Functions -- Qualifiers

• inline Member Functions
  • Function Bodies are Substituted for the Function Call At Compile Time
  • All the Member Functions Defined within the Class Definition are Implicitly Inline
  • If Defined Outside the Class Definition, inline Qualifier is Required
  • Faster Execution
• static Member Functions
  • Exist Before Any Class Instantiation -- Access Only the Static Class Members
• const Member Functions
  • CANNOT Change Data Members
  • The ONLY ONE that can Process Constant Objects
  • Can also Process Non-Constant Objects

Nested Classes

• A Class Contained in Another Class

• Multiple Levels of Nesting Are Allowed

• Usual Scoping Rules Apply

• class one{ //Class "two" is nested inside the class "one"Nested Classes -- Example

int a; public: class two{ int b; public: two(){b = 10;} void print_b() {cout << "two's b: " << b << endl;} }; two one_two;

• one(){a = 100;} void print_a() {cout << "one's a: " << a << endl;} };

Constant Data Members

• Principle of least privilege

• Only give objects permissions they need, no more

• Keyword const

• Specify that an object is not modifiable
• Any attempt to modify the object is a syntax error
• Example const Time noon( 12, 0, 0 );
• Declares a const object noon of class Time and initializes it to 12

Constant Member Functions

• const objects require const functions
  • Member functions declared const cannot modify their object
  • const must be specified in function prototype and definition
  • Prototype: ReturnType FunctionName(param1,param2…) const;
  • Definition: ReturnType FunctionName(param1,param2…) const { …}
  • Example: int A::getValue() const { return privateDataMember };
• Returns the value of a data member but doesn’t modify anything so is declared const
• Constructors / Destructors cannot be const
  • They need to initialize variables, therefore modifying them

const -- Example

• class student{ int ss, credits; public: student():ss(0), credits(0){} //const member function cannot modify the data member int get_ss() const {return ss;} int get_credits(){return credits;} };
• main(){ student s1; const student s2; s1.get_ss(); s1.get_credits(); s2.get_ss(); //constant object s2.get_credits(); //ERROR!!! Cannot call a non-constant function }